Mass spectrometry (MS) is an analytical technique that measures the mass-to-charge ratio of charged particles. It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and other chemical compounds. The MS principle consists of ionizing chemical compounds to generate charged molecules or molecule fragments and measurement of their mass-to-charge ratios.
In a typical MS procedure, a sample is loaded onto the MS instrument and undergoes vaporization. The components of the sample are ionized by one of a variety of methods (e.g., by impacting them with an electron beam), which results in the formation of charged particles (ions). The ions are separated according to their mass-to-charge ratio in a mass analyzer by electromagnetic fields. The ions are detected, usually by a quantitative method. The ion signal is processed into mass spectra.
FIG. 1 shows a block diagram of prior art MS instrument. The mass spectrometer comprises an ion source that generates and supplies ions to be analyzed to a set of ion optics including an ion guide are used to send the ions to the analyzer. Ion optics may be located adjacent to the ion guide so that mass spectra may be taken, under the direction of the controller. The mass spectrometer, as a whole, is operated under the direction of the controller. The mass spectrometer is generally located within a vacuum chamber provided with one or more pumps to evacuate its interior.
Ion storage devices that use RF fields for transporting or storing ions have become standard in mass spectrometers. One ion guide is the humpbacked ion guide, shown in FIG. 2 and FIG. 2B, is efficient in blocking neutrals/particles to prevent ion spikes due to debris. The elongate electrodes extend along a curved axis, the electrodes being paired in the x and y axes, e.g. 0°, 90°, 180°, and 270°. Unfortunately, there is accumulation of contaminants on rising section of the curved ion guide, e.g. the surface of electrode at 270° that tends to degrade the performance of the device over time. As the device does not allow for a good pumping out of the gas flow coming from the previous chamber, downstream optics, e.g. the ion optics can also become contaminated.
FIG. 3A and FIG. 3B shows an alternate arrangement of four electrodes in a curved ion guide device that confines and transfers ions using a combination of DC, RF, and AC fields. The elongate electrodes extend along a curved axis, the electrodes being paired in the x and y axes, e.g. 0°, 90°, 180°, and 270°. In addition to the ions, the ion optics are contaminated by additional debris, e.g. neutrals, particles, or charged droplets. The static charge from the debris builds up on the ion optics thereby degrading performance of the device over time.